1. Field of the Invention:
This invention relates to the production of glycosides by the reaction of an alcohol with a reducing saccharide, or a source of reducing saccharide, in the presence of an acid catalyst.
2. Statement of Related Art:
The reaction of a reducing saccharide, e.g. an aldose or ketose saccharide, or a source thereof, with an alcohol results in the formation of a glycoside. Acids catalyze the reaction between a reducing saccharide and an alcohol. When the alcohol is an alkanol, the resulting glycoside is commonly referred to as an alkyl glycoside. Alkyl glycosides are generally stable to alkali. Long chain alkyl groups contribute to surface activity, e.g. detergency, of the glycoside.
U.S. Pat. No. 3,547,828 (Mansfield et al.) discloses a process for producing surface active (i.e. higher alkyl) glycosides by first reacting a saccharide with a lower alkanol (e.g. butanol) in the presence of an acid catalyst to form a lower alkyl glycoside which is then reacted with a higher alkanol to form the higher alkyl glycoside. The acid catalysts disclosed by Mansfield et al. are mineral acids (H.sub.2 SO.sub.4, HCl and HNO.sub.3), p-toluenesulfonic acid, and methanesulfonic acid. It is stated by Mansfield et al. that while other acid, electron accepting compounds of the group generally classified as "Lewis acids" may be employed as catalysts, sulfuric acid is preferred.
U.S. Pat. No. 3,598,865 (Lew) discloses the production of higher alkyl (C.sub.8 -C.sub.25) glycosides from a monosaccharide or source thereof and a higher monohydric alcohol in the presence of a latent solvent (lower alcohols) and an acid catalyst selected from the group consisting of sulfuric acid, hydrochloric acid, phosphoric acid, phosphorous acid, toluenesulfonic acid, and boron trifluoride.
U.S. Pat. No. 3,219,656 (Boettner) discloses a process for producing a higher alkyl glycoside by reacting glucose with methanol in the presence of a macroreticular-structured sulfonic acid resin, anhydrous and in the acid form, to produce methyl glucoside which is reacted without isolation with butanol to form butyl glucoside and which in turn is reacted with a higher alcohol to form a surface active higher alkyl glycoside.
U.S. Pat. No. 3,839,319 (Mansfield) discloses a process for producing alkyl glycosides by direct, acid catalyzed reaction of a higher alcohol and a saccharide. The acid catalysts are mineral acids such as hydrochloric and sulfuric, and sulfonic acid exchange resins.
E.P.O. Publication No. 132,043, published Jan. 23, 1985, (Davis et al.) discloses the production of alkyl glycosides by reacting, in the presence of an acid catalyst, a monohydric alcohol with a monosaccharide or a source thereof, wherein the acid catalyst is the acid form of an anionic surfactant, e.g. alkyl hydrogen sulfates or alkyl sulfonic acids having in their molecular structure an alkyl group containing from 8 to 22 carbon atoms and alkylbenzene sulfonic acid, with alkyl groups having from 8 to 15 carbon atoms. The publication states it is contemplated by Davis et al. that the catalyst gives a faster reaction rate by building up on the surface of solid saccharide particles which is facilitated by the surface active properties of the catalyst.
While the above processes have varying degrees of utility, they each suffer from one or more disadvantages such as inefficient multi-phase reactions, insufficient reaction rates, excessive by-product formation (e.g. polydextrose), excessive color formation, as well as others. Accordingly, it is desirable to provide a new process which does not suffer from one or more of the disadvantages in the above processes.